Field of the Invention
The invention is in the field of coupling optical and electro optical elements and, in particular, coupling an optical fiber end to an electro optical component. The invention also relates to a method for producing an electro optical module which has on the front side a coupling socket for holding an optical fiber end, and at the rear a holding region for an electro optical component, in which the electro optical component is brought into a position of maximum optical coupling with the optical fiber end held by the coupling socket, and in which the component is connected in this position to the holding region by an adhesive.
Within the scope of the present invention, an electro optical component is to be understood both as an optical transmitter (e.g. laser diode) and as a receiver (e.g. photodiode), which converts electric signals into optical ones and/or optical signals into electrical ones (optoelectronic transducer).
With electro optical modules, the aim is to ensure that the coupling efficiency between the coupling partners is as high as possible. For this purpose, it is necessary, for example, for the optical fiber end to be aligned with high precision with reference to the optically active surface (emitting or receiving surface, respectively) of the electro optical component. A lens can be disposed in the beam path between the optical fiber end and electro optical component. There is frequently the need for a demountable coupling of the optical fiber end, the optical fiber end usually being held in a central bore in a plug pin. The plug pin is inserted for coupling purposes into the coupling socket and removably fixed in the inserted position. In order to ensure a high coupling Q-factor even with regard to different combinations of coupling partners, the electro optical component must be fixed with high precision with reference to the coupling socket and therefore, indirectly, to the coupling partner to be held by the coupling socket, and in a way which is stable in the long term. Laser welding methods, which offer very good method results in conjunction with comparatively short machining periods can be applied for fixing purposes. In this case, the weldable components are, however, very restricted with regard to the choice of material, and are comparatively expensive. The devices and welding systems required to carry out the method also necessitates high investment.
It is for this reason that increasing use has been made of adhesives for connection, in particular for the purpose of producing cost-effective electrooptical modules. Favorably priced individual parts, for example made from plastic, can thereby be used.
Published European Patent Application EP 0 351 211 A2 discloses a method for producing an optical plug pin which simultaneously forms a housing for completely holding an electrooptical transducer configuration. In this case, the transducer configuration is introduced into a mold, surrounded by a sealing material that can be cured by light and/or heat, and fixed by curing the sealing material after alignment with a reference plug. A plug pin is created after removal from the mold, the transducer configuration being positioned precisely with reference to the concentric plug pin lateral surface.
A method of the type mentioned at the beginning has been disclosed in German Patent DE 43 11 980 C1. According to the known method, a module having a front sleeve for holding a plug pin and having a rear holding space for a laser diode is produced by using an optically curing adhesive. For the purpose of aligning the laser diode, a plug pin with an optical fiber end is inserted up to a stop, and the light emitted when the laser diode is driven is launched into the optical fiber end and evaluated with respect to its intensity at the other optical fiber end. By displacing the component relative to the laser diode, the optimum coupling position is determined by evaluating the intensity. The adhesive is cured in this position (so-called "active adjustment"). However, with reference to the curing of the adhesive there is a need in this case to make use, in a fashion limiting the choice of material, of transparent materials for the holding region (holder) and/or to occupy the production equipment for a comparatively long time, at least until the adhesive has reached a basic strength which permits the semi-finished module to be removed. With regard to these problems, it is conceivable to make simultaneous use of a plurality of adhesives, a first, quickly curing adhesive ensuring prefixing. However, in this case additional production difficulties and partly contrary optimization goals arise. Thus, there would be a need for multiple application of adhesive. Furthermore, although highly filled adhesives have mechanically favorable properties, they can impair the curing of the quickly curing adhesive.